Electro-Magnetic Experiments. 381 



of the machinery of a dipping needle ; but oscillations can be obtain- 

 ed at various points by which the tendency may be ascertained. 

 Temporary balances may be applied at any point to counteract the 

 imperfections of the machinery. 



The experiment of the dipping ring is so strongly indicated by ma- 

 ny other experiments that I think it probable it has been made ; but 

 I have seen no account of it. 



III. Additional Experiments, April 21 rf, 1834. 



Finding my discoid galvanometer to be a very delicate indicator of 

 thermo-electricity, I have been able to attempt to ascertain the ther- 

 mo-electric powers of all of the metals, by experiments similar to 

 those of Prof. Emmet detailed in the last number of the Journal of 

 Science. 



Whilst I enter the same field of original investigation with the dis- 

 tinguished philosopher just named, and arrive at conclusions in some 

 points slightly different from his, let it be understood that 1 regard 

 his labor and discoveries with no other sentiment, than that of admi- 

 ration. 



My object was chiefly, to form a scale of the thermo-electric pow- 

 ers, of the several simple metals as indicated by the galvanometer, 



»/ 



are placed in 



contact. In order to do this in the most unexceptionable manner, I 

 made the following preliminary experiments. 



1st. I made a circuit of copper wire six feet long and connected 

 its extremities with the poles of the galvanometer. To this wire I 

 applied the flame of a spirit lamp and moved it rapidly along from 

 one point to another to ascertain whether the more progressive mo- 

 tion of heat in metal was a cause of an electrical current. No elec- 

 tricity was indicated by the needle. 



2d. Cutting the same wire in the middle, and connecting the cut 

 ends by twisting them together, I applied the flame of a spirit lamp 

 close to one side of the joint. The needle of the galvanometer was 

 turned 10 deg. in 33 seconds, and 20 deg. in 48 seconds, in such di- 

 rection as to indicate a current of electricity passing through the joint 

 from the heated side. 



3d. To acertain whether the rupture of the wire produced any ef- 

 fect when the heat did not reach it I applied the lamp to a point re- 

 mote from it. No motion of the needle followed. 



4th. To ascertain whether the connexion of my apparatus with 

 the galvanometer by means of mercury cups, or solder would influ- 



